Intermolecular Binding Energy Research Articles

Effects and molecular mechanisms of jet ablation and fuel corrosion on separation failure of the asphalt-aggregate interface in airport asphalt pavements

To guide the improvement of asphalt pavement durability in airports, the effects and molecular mechanisms of jet ablation and fuel corrosion on separation failure of the asphalt-aggregate interface were investigated in this study using molecular dynamics simulations and density functional theory method. Firstly, tensile separation behaviors of the virgin, aged, and fuel-corroded asphalt-aggregate interfaces were simulated under different loading rates to evaluate their tensile strength and fatigue cracking resistance, and the experimental data were also used to verify the reliability of the simulation results. Subsequently, the molecular mechanisms of jet ablation and fuel corrosion on the separation failure of the asphalt-aggregate interface were analyzed by calculating the work of adhesion, work of cohesion, flowability parameters, and intermolecular binding energy. The results show that the aged specimen has higher ultimate tensile strength and fracture energy, but its flexibility and fatigue cracking resistance are significantly reduced. This is because the polar oxygen-containing groups generated during high-temperature aging enhance the intermolecular binding energy of the asphalt, but this also restricts the diffusion of asphalt molecules, resulting in greater frictional resistance and viscosity of asphalt during shear deformation, and thus loss of mobility and self-healing properties. On the contrary, since the light and medium oils soften and dilute the asphalt, and also weaken the intermolecular binding energy of asphalt, the fuel corrosion reduces the ultimate tensile strength and fracture energy of the asphalt-aggregate interface system, resulting in insufficient overall strength and load-bearing capacity.

Computational exploration and design of a multi-epitopes vaccine construct against Chlamydia psittaci

Chlamydia psittaci is an intracellular pathogen and causes variety of deadly infections in humans. Antibiotics are effective against C. psittaci however high percentage of resistant strains have been reported in recent times. As there is no licensed vaccine, we used in-silico techniques to design a multi-epitopes vaccine against C. psittaci. Following a step-wise protocol, the proteome of available 26 strains was retrieved and filtered for subcellular localized proteins. Five proteins were selected (2 extracellular and 3 outer membrane) and were further analyzed for B-cell and T-cell epitopes prediction. Epitopes were further checked for antigenicity, solubility, stability, toxigenicity, allergenicity, and adhesive properties. Filtered epitopes were linked via linkers and the 3D structure of the designed vaccine construct was predicted. Binding of the designed vaccine with immune receptors: MHC-I, MHC-II, and TLR-4 was analyzed, which resulted in docking energy scores of −4.37 kcal/mol, −0.20 kcal/mol and −22.38 kcal/mol, respectively. Further, the docked complexes showed stable dynamics with a maximum value of vaccine-MHC-I complex (7.8 Å), vaccine-MHC-II complex (6.2 Å) and vaccine-TLR4 complex (5.2 Å). As per the results, the designed vaccine construct reported robust immune responses to protect the host against C. psittaci infections. In the study, the C. psittaci proteomes were considered in pan-genome analysis to extract core proteins. The pan-genome analysis was conducted using bacterial pan-genome analysis (BPGA) software. The core proteins were checked further for non-redundant proteins using a CD-Hit server. Surface localized proteins were investigated using PSORTb v 3.0. The surface proteins were BLASTp against Virulence Factor Data Base (VFDB) to predict virulent factors. Antigenicity prediction of the shortlisted proteins was further done using VAXIGEN v 2.0. The epitope mapping was done using the immune epitope database (IEDB). A multi-epitopes vaccine was built and a 3D structure was generated using 3Dprot online server. The docking analysis of the designed vaccine with immune receptors was carried out using PATCHDOCK. Molecular dynamics and post-simulation analyses were carried out using AMBER v20 to decipher the dynamics stability and intermolecular binding energies of the docked complexes. Communicated by Ramaswamy H. Sarma

Electron density-based protocol to recover the interacting quantum atoms components of intermolecular binding energy.

A new approach for obtaining interacting quantum atoms-defined components of binding energy of intermolecular interactions, which bypasses the use of standard six-dimensional integrals and two-particle reduced density matrix (2-RDM) reconstruction, is proposed. To examine this approach, three datasets calculated within the density functional theory framework using the def2-TZVP basis have been explored. The first two, containing 53 weakly bound bimolecular associates and 13 molecular clusters taken from the crystal, were used in protocol refinement, and the third one containing other 20 bimolecular and three cluster systems served as a validation reference. In addition, to verify the performance of the proposed approach on an exact 2-RDM, calculations within the coupled cluster formalism were performed for part of the first set systems using the cc-pVTZ basis set. The process of optimization of the proposed parametric model is considered, and the role of various energy contributions in the formation of non-covalent interactions is discussed with regard to the obtained trends.

Complex peptide macrocycle optimization: combining NMR restraints with conformational analysis to guide structure-based and ligand-based design

Systematic optimization of large macrocyclic peptide ligands is a serious challenge. Here, we describe an approach for lead-optimization using the PD-1/PD-L1 system as a retrospective example of moving from initial lead compound to clinical candidate. We show how conformational restraints can be derived by exploiting NMR data to identify low-energy solution ensembles of a lead compound. Such restraints can be used to focus conformational search for analogs in order to accurately predict bound ligand poses through molecular docking and thereby estimate ligand strain and protein-ligand intermolecular binding energy. We also describe an analogous ligand-based approach that employs molecular similarity optimization to predict bound poses. Both approaches are shown to be effective for prioritizing lead-compound analogs. Surprisingly, relatively small ligand modifications, which may have minimal effects on predicted bound pose or intermolecular interactions, often lead to large changes in estimated strain that have dominating effects on overall binding energy estimates. Effective macrocyclic conformational search is crucial, whether in the context of NMR-based restraints, X-ray ligand refinement, partial torsional restraint for docking/ligand-similarity calculations or agnostic search for nominal global minima. Lead optimization for peptidic macrocycles can be made more productive using a multi-disciplinary approach that combines biophysical data with practical and efficient computational methods.

Multitargeted pharmacokinetics, molecular docking and network pharmacology-based identification of effective phytocompounds from Sauropus androgynus (L.) Merr for inflammation and cancer treatment

According to worldwide health data, cancer, and inflammatory illnesses are on the rise and are among the most common causes of death. Across the world, these types of health problems are now considered top priorities for government health organizations. Hence, this study aimed to investigate medicinal plants’ potential for treating cancer and inflammatory disorders. This network pharmacology analysis aims to learn more about the potential targets and mechanisms of action for the bioactive ingredients in Sauropus androgynus (L.) Merr L. The compound-target network and protein-protein interaction analysis were built using the STRING database. Using Network Analyst, Gene Ontology, and Kyoto Encyclopaedia of Genes and Genomes, pathway enrichment was performed on the hub genes. 1-hexadecanol was shown to inhibit drug-metabolizing enzymes in a pharmacokinetic investigation. Those samples of 1-hexadecanol were found to be 1-hexadecanol (BBB 0.783), GI High, Pgp Substrate Yes, CYP2C19 Inhibitor Yes, CYP2D6 Yes, and HI −89.803. The intermolecular binding energies for 1-hexadecanol (4-DRI, −8.2 kcal/mol) are evaluated. These results from a study on S. androgynus used molecular docking and network pharmacology to gain insight into the prime target genes and potential mechanisms identified for AKT1, mTOR, AR, PPID, FKBP5, and NR3C1. The PI3K-Akt signalling pathway has become an important regulatory node in various pathological processes requiring coordinated actions. Stability and favourable conformations have been resolved by considering nonbonding interactions such as electrostatic and hydrogen bonds in MD simulations of the perfect molecules using the Desmond package. Thus, using an appropriate platform of network pharmacology, molecular docking, and in vitro experiments, this study provides for the first time a clearer knowledge of the anti-cancer and anti-inflammatory molecular bioactivities of S. androgynus. Further in vitro and in vivo confirmations are strongly needed to determine the efficacy and therapeutic effects of 1-hexadecanol in the biological process. Communicated by Ramaswamy H. Sarma

Dye spectra of benzene derivatives in the liquid-crystalline phase of 4-n-pentyl-4΄-cyanobiphenyl.

In the present paper, we study the interaction of associates (dimers and trimers) of 4-n-pentyl-4΄-cyanobiphenyl (5CB) with 1, 2-Diamino-4-nitrobenzene and N, N-Dimethyl-4-nitrosoaniline dye molecules. The structures of the intermolecular complexes were studied using hybrid functionals of the DFT method M06 and B3LYP with the 6-31 + G (d) basis set. The intermolecular binding energy of dyes with associates depends on the structure of the complexes and is about 5kcal/mol. Vibrational spectra were calculated for all intermolecular systems. The electronic absorption spectra of dyes are sensitive to the structure of the mesophase. The pattern of the spectrum changes depending on the structure of the complex of the dimer or trimer with the dye molecule. The long-wavelength transition bands are characterized by shifts that are bathochromic for 1, 2-Diamino-4-nitrobenzene and hypsochromic for N, N-Dimethyl-4-nitrosoaniline.

Study on Mechanical Properties of Two-Component Polyurethane Based on Multi-Scale Molecular Simulation.

Mechanical properties determine the use of two-component polyurethane materials. The compatibility of two components in the polyether polyol-MDI molecular system greatly influences the formation of mechanical properties in polyurethane materials. In this paper, we studied and evaluated the compatibility and mechanical properties of two-component polyurethane at multiple scales by combining molecular dynamics simulation with macroscopic experiments, which is an important guideline for synthesizing and preparing two-component polyurethanes. We evaluated the stability of the two-component polyurethane system by calculating the solubility parameter, binding energy, and diffusion coefficient at four temperatures with three isocyanate contents. The Perl scripting language obtained the mechanical properties of the MDI-polyether polyol system. The MD calculation results show that the solubility parameter of two-component polyurethane negatively correlated with temperature, and the intermolecular binding energy and MDI diffusion coefficient positively correlated with temperature. When the mass ratio of polyether polyol to isocyanate was 1:0.6, the solubility parameter difference between the two was 1.43 (J/cm3)1/2, the intermolecular binding energy was 531.68 kcal/mol, and the two-component system was more stable. A macroscopic direct tensile test was employed to assess the polyurethane elastomers' tensile properties. Our results show that the tensile strength of polyurethane elastomers increased with the increase in isocyanate content and decrease in temperature. Furthermore, the elongation at the break decreased, and the modulus increased, which is consistent with the law of molecular simulation.

Study on the storage stability performance enhancement mechanism of graphene on rubber-modified asphalt based on size effect

<abstract> <p>The application of waste rubber powder (WRP) for asphalt pavement could achieve the harmless and resourceful utilization of solid waste, but the storage stability of waste rubber powder modified asphalt (RA) is one of the main problems restricting its application. Existing studies have demonstrated that graphene could enhance the storage stability of RA, but graphene's size effect on the modifying effect and its corresponding mechanism are still uncertain. In this research, the effects of graphene microstructural properties (i.e., molecular size and layer number) on the storage stability of RA were investigated by storage stability testing, dynamic shear rheometry (DSR) testing and fluorescence microscopy (FM) testing, in combination with molecular dynamics simulation (MD). The experimental results indicated that graphene improved the storage stability of RA significantly, with few-layer graphene being more effective in enhancing it. MD was used to investigate the graphene size effect on RA in compatibility, intermolecular binding energy and structural stability of the system. The simulation results revealed that small-sized graphene molecules were more compatible with RA. Meanwhile, few-layer, small-sized graphene can provide higher binding energy and better enhancement of storage stability of RA. The number of graphene layers mainly influences the binding energy rather than solubility parameters. The relative concentration distribution results demonstrated that graphene facilitated the spatial distribution of asphaltenes, rubber components and light components. This research provides theoretical support for the rational selection of microstructural properties of graphene to improve the modified asphalt storage stability performance.</p> </abstract>

Comparative antibacterial analysis of the anthraquinone compounds based on the AIM theory, molecular docking, and dynamics simulation analysis.

Hydroxyanthraquinones and anthraquinone glucoside derivatives are always considered as the active antibacterial components. Comparison of structure characteristics and antibacterial effect of these compounds was performed by applying quantum chemical calculations, atoms in molecules theory, molecular docking, and dynamics simulation procedure. Density functional theory calculation with B3LYP using 6-31G (d, p) basis set has been used to determine ground state molecular geometries. The molecular geometric stability, electrostatic potential, frontier orbital energies, and topological properties were analyzed at the active site. Once glucose ring is introduced into the hydroxyanthraquinone rings, almost all of the positive molecular potentials are distributed among the hydroxyl hydrogen atoms of the glucose rings. In addition, low electron density ρ (r) and positive Laplacian value of the O-H bond of the anthraquinone glucoside are the evidences of the highly polarized and covalently decreased bonding interactions. The anthraquinone glucoside compounds have generally higher intermolecular binding energies than the corresponding aglycones due to the strong interaction between the glucose rings and the surrounding amino acids. Molecular dynamics simulations further explored the stability and dynamic behavior of the anthraquinone compound and protein complexes through RMSD, RMSF, SASA, and Rg. The type of carboxyl, hydroxyl, and hydroxymethyl groups on phenyl ring and the substituent glucose rings is important to the interactions with the topoisomerase type II enzyme DNA gyrase B.

A Cost Effective Scheme for the Highly Accurate Description of Intermolecular Binding in Large Complexes.

There has been a growing interest in quantitative predictions of the intermolecular binding energy of large complexes. One of the most important quantum chemical techniques capable of such predictions is the domain-based local pair natural orbital (DLPNO) scheme for the coupled cluster theory with singles, doubles, and iterative triples [CCSD(T)], whose results are extrapolated to the complete basis set (CBS) limit. Here, the DLPNO-based focal-point method is devised with the aim of obtaining CBS-extrapolated values that are very close to their canonical CCSD(T)/CBS counterparts, and thus may serve for routinely checking a performance of less expensive computational methods, for example, those based on the density-functional theory (DFT). The efficacy of this method is demonstrated for several sets of noncovalent complexes with varying amounts of the electrostatics, induction, and dispersion contributions to binding (as revealed by accurate DFT-based symmetry-adapted perturbation theory (SAPT) calculations). It is shown that when applied to dimeric models of poly(3-hydroxybutyrate) chains in its two polymorphic forms, the DLPNO-CCSD(T) and DFT-SAPT computational schemes agree to within about 2 kJ/mol of an absolute value of the interaction energy. These computational schemes thus should be useful for a reliable description of factors leading to the enthalpic stabilization of extended systems.

Stable nanovesicles formed by intrinsically planar bilayers

HypothesisQuatsome nanovesicles, formed through the self-assembly of cholesterol (CHOL) and cetyltrimethylammonium bromide (CTAB) in water, have shown long-term stability in terms of size and morphology, while at the same time exhibiting high CHOL-CTAB intermolecular binding energies. We hypothesize that CHOL/CTAB quatsomes are indeed thermodynamically stable nanovesicles, and investigate the mechanism underlying their formation. ExperimentsA systematic study was performed to determine whether CHOL/CTAB quatsomes satisfy the experimental requisites of thermodynamically stable vesicles. Coarse-grain molecular dynamics simulations were used to investigate the molecular organization in the vesicle membrane, and the characteristics of the simulated vesicle were corroborated with experimental data obtained by cryo–electron microscopy, small- and wide-angle X-ray scattering, and multi-angle static light scattering. FindingsCHOL/CTAB quatsomes fulfill the requisites of thermodynamically stable nanovesicles, but they do not exhibit the classical membrane curvature induced by a composition asymmetry between the bilayer leaflets, like catanionic nanovesicles. Instead, CHOL/CTAB quatsomes are formed through the association of intrinsically planar bilayers in a faceted vesicle with defects, indicating that distortions in the organization and orientation of molecules can play a major role in the formation of thermodynamically stable nanovesicles.

Systemic computational investigation to identify potential inhibitors against cancer by targeting P21-activated kinase 4 and D(CGATCG)

Cancer accounts for more than 10 million deaths in the year 2020. Development of drugs that specifically target cancer signaling pathways and proteins attain significant importance in the recent past. The p21-activated kinase 4 enzyme, which plays diverse functions in cancer and is reported in elevated expression makes this enzyme an attractive anti-cancer drug target. Similarly, cancer cells’ DNA could also serve as a good platform for anti-cancer drug development. Herein, a robust in silico framework is designed to virtually screen multiple drug libraries from diverse sources to identify potential binders of the mentioned cancer targets. The virtual screening process identified three compounds (BAS_01059603, ASN_10027856, and ASN_06916672) as best docked molecules with a binding energy score of ≤ −10 kcal/mol for p21-activated kinase 4 and ≤ −6 kcal/mol for D(CGATCG). In the docking analysis, the filtered compounds revealed stable binding to the same site to which controls bind in X-ray structures. The binding interactions of the compounds with receptors are dominated by van der Waals interactions. The average root mean square deviation (rmsd) value for p21-activated kinase 4 systems is noticed at ∼2 Å, while for D(CGATCG), the average rmsd is 2.7 Å. The MMGB/PBSA interpreted ASN_12674021 to show strong intermolecular binding energy compared to the other two systems and control in both receptors. Moreover, the entropy energy contribution is less than the mean binding energy. In short, the compounds are showing promising binding to the biomolecules and therefore must be evaluated for anti-cancer activity in experimental studies. Communicated by Ramaswamy H. Sarma

Computational Design of a Multi-Epitope Vaccine Against Porphyromonas gingivalis.

Porphyromonas gingivalis is a Gram-negative pathogenic bacterium associated with chronic periodontitis. The development of a chimeric peptide-based vaccine targeting this pathogen could be highly beneficial in preventing oral bone loss as well as other severe gum diseases. We applied a computational framework to design a multi-epitope-based vaccine candidate against P. gingivalis. The vaccine comprises epitopes from subunit proteins prioritized from the P. gingivalis reference strain (P. gingivalis ATCC 33277) using several reported vaccine properties. Protein-based subunit vaccines were prioritized through genomics techniques. Epitope prediction was performed using immunoinformatic servers and tools. Molecular modeling approaches were used to build a putative three-dimensional structure of the vaccine to understand its interactions with host immune cells through biophysical techniques such as molecular docking simulation studies and binding free energy methods. Genome subtraction identified 18 vaccine targets: six outer-membrane, nine cytoplasmic membrane-, one periplasmic, and two extracellular proteins. These proteins passed different vaccine checks required for the successful development of a vaccine candidate. The shortlisted proteins were subjected to immunoinformatic analysis to map B-cell derived T-cell epitopes, and antigenic, water-soluble, non-toxic, and good binders of DRB1*0101 were selected. The epitopes were then modeled into a multi-epitope peptide vaccine construct (linked epitopes plus adjuvant) to enhance immunogenicity and effectively engage both innate and adaptive immunity. Further, the molecular docking approach was used to determine the binding conformation of the vaccine to TLR2 innate immune receptor. Molecular dynamics simulations and binding free energy calculations of the vaccine–TLR2 complex were performed to highlight key intermolecular binding energies. Findings of this study will be useful for vaccine developers to design an effective vaccine for chronic periodontitis pathogens, specifically P. gingivalis.

Phase separation and intermolecular binding energy of ibuprofen in some organic solvents

The capacity of water-insoluble drug solution to endure its phase inversion influenced by water induction, water tolerance, was measured by using the titration method. The water tolerance of ibuprofen (IBU) solutions using ethanol, dimethyl sulfoxide, and N-methyl-2-pyrrolidone as the solvents was investigated for understanding their phase separation behaviors. The IBU solutions were titrated with distilled water and found that the water tolerance was affected with the content of IBU, type of solvent, and system temperature. Namely, IBU in ethanol (IE) solution showed a higher water tolerance than IBU in NMP solution (IN) and IBU in DMSO (ID). The water tolerance value of these IBU solutions at 37 °C was notably higher than that at room temperature. The phase separation rate of ID was higher than IN and IE, respectively. Thereafter, the H-bonding interactions and the binding energy between IBU and these organic solvents were investigated using density-functional theory (DFT) calculations. The binding energy between solvent in IE was apparently lower than those of IN and ID, respectively, indicated that solvent–solvent bonding could influence the water tolerance of the IBU solution. The relationship between phase separation property and binding energy provides the useful information for further development IBU solution as the in situ forming system with aqueous sensitive-induced phase transition mechanism which the solution phase changes itself into solid/semi-solid state for controlled drug release.

Unraveling oxidative aging behavior of asphaltenes using ab initio molecular dynamics and static density functional theory

Asphalt aging is a major cause of cracking failure in asphalt pavement. However, owing to the lack of understanding of the asphalt aging mechanism, research on asphalt-targeted antiaging technology has encountered challenges. To address this issue, ab initio molecular dynamics simulations and density functional theory calculations based on the quantum chemistry framework were conducted to explore the reaction pathway and thermodynamic driving force of asphaltene aging. The physical properties of asphaltenes were evaluated to determine the effect of aging on asphaltene performance. The results indicate that asphaltenes undergo aging subreactions at different temperatures, including aromatization of naphthenes, formation of oxygen-containing groups, and homolysis of alkyl side chains. The free energy barriers of these reactions can be ranked in ascending order as aromatization < oxygen-containing group formation < homolysis. The molecular polarity, intermolecular binding energy, and solubility parameter of the asphaltene molecule increased significantly with aging, leading to enhanced agglomeration and reduced compatibility of asphalt components, resulting in the deterioration of asphalt cracking resistance.

Computational Studies of Uranium Hexafluoride Interacting with Functionalized Organics. I. Screening Intermolecular Potentials between UF6 and Small Organic Functional Groups.

We report the intermolecular binding energies (IBEs) between UF6 and over 50 different functionalized small organic molecules as predicted by electronic structure calculations. Optimized geometries of UF6-molecule dimers were found at the MP2/aug-cc-pwCVDZ (non-U), cc-pVDZ-PP (U) level. IBEs were calculated using MP2 and dispersion-corrected DFT theory. We characterize the various functional groups based on the inclusion of specific heteroatoms. Those functional groups containing "nitrogen only" heteroatoms result in larger IBEs than groups containing both nitrogen and oxygen or oxygen alone. Halogen-containing and regular hydrocarbon molecules show the lowest IBEs with UF6. Nonorganic phosphoryl species are also shown to display large IBEs with UF6. These interactions are characterized in part by how much the impinging functionalized molecule distorts the UF6 from its optimal octahedral geometry. Of all the investigated groups, the amine group displayed the largest IBE values (IBE ∼ >12-14 kcal/mol for methyl amine), while hydrocarbons and perfluorocarbons both showed the weakest interactions (IBE ∼ 0.5-1.5 and 0.1-0.8 kcal/mol for methane and perfluoromethane, respectively). The study examines how the strength of the IBE is contingent on a combination of conformational deformation, stabilizing nonbonding interactions, and sterics.

Nonlabeled detection of specific intermolecular bondings by terahertz surface plasmon resonance of topological insulator.

The terahertz (THz) band, which corresponds to intermolecular binding energy, is the key to achieving a nonlabeled biosensor. To realize high-sensitivity binding detection, we focused on surface plasmon resonance (SPR) in the THz range. Using THz-SPR enhanced a in topological insulator, we expect to observe the synergistic effects of two resonance phenomena, namely intermolecular vibrational resonance and SPR. In this Letter, we report the nonlabeled detection of biomolecular binding by the topological insulator THz-SPR. Bi2Se3 was processed in a microribbon array to enhance the SPR in the THz range. The avidin-biotin specific binding, which is similar to the antigen-antibody reaction mechanism and has powerful interactions, was observed owing to enhancement by Bi2Se3 THz-SPR. This work paves the way for a system to directly measure specific molecular bonds using topological insulators.

Understanding solid-state processing of pharmaceutical cocrystals via milling: Role of tablet excipients

Discovery of novel cocrystal systems and improvement of their physicochemical properties dominates the current literature on cocrystals yet the required end-product formulation is rarely addressed. Drug product manufacturing includes complex API solid state processing steps such as milling, granulation, and tableting. These all require high mechanical stress which can lead to solid-state phase transformations into polymorphs and solvates, or lead to dissociation of cocrystals into their individual components. Here we measured the effect of tablet excipients on solid-state processing of a range of pharmaceutical cocrystal formulations. Our findings were rationalised using Density Functional Theory (DFT) calculations of intermolecular binding energies of cocrystal constituents and co-milling excipients. A 1:1 stoichiometric ratio of API Theophylline (THP) and co-former 4-Aminobenzoic acid (4ABA) was co-milled with five different excipients: hydroxypropylmethylcellulose (HPMC), polyvinylpyrrolidone (PVP), polyethylene glycol (PEG), lactose, and microcrystalline cellulose (MCC). The experiments were carried out in 10 and 25 ml milling jars at 30 Hz for different milling times. Co-milled samples were characterised for formation of cocrystals and phase transformation using powder X-ray diffraction (PXRD) and differential scanning calorimetry (DSC). Our data shows that co-milling in the presence of PEG, HMPC or lactose yields purer cocrystals, supported by the calculated stronger excipient interactions for PVP and MCC. We identify a suitably-prepared THP–4ABA pharmaceutical cocrystal formulation that is stable under extended milling conditions.

Conformational behavior of naphtho-merocyanine dimers on Au(111)

Thin film growth of molecules on substrates are governed by the convolution of inter-molecular forces and template-adsorbate interactions. Often the initial dimer formation plays a crucial role in the outcome of the molecular structure on the surface. Here, the behavior of naphtho-merocyanine on an Au(111) substrate was investigated using computational chemistry methods and Scanning Tunneling Microscopy. The experiments show a strong preference of dimer formation of the merocyanine molecules. Topographical measurements are used to identify two distinguished configurations, an elongated/oval dimer and a compact/rectangular dimer. With the addition of computational chemistry calculations including Density Functional Theory (DFT) and Molecular Mechanics calculations using the AMBER 3 force field, these two configurations of two specific merocyanine conformers, namely CTC and CTT, could be identified. Intermolecular binding energy calculations could be performed. This is a first step in understanding the possible island/thin film growth of naphtho-merocyanine and subsequently possible pathways toward the switching behavior of merocyanine and spiropyran on this substrate.

Self‐Assembly Method for Insensitive DAAF/FOX‐7 Composite Crystals with Microspheres Structure

AbstractHighly efficient design for the formulation of explosives is desired for accelerating the development of energetic materials. These investigations are focused on the preparation of the compounds 3,3′‐diamino‐4,4′‐azoxyfurazan (DAAF) and 1,1‐diamino‐2,2‐dinitroethylene (FOX‐7). DAAF/FOX‐7 microspheres are prepared via the self‐assembly method using different mass ratios of DAAF and FOX‐7. Materials Studio is used to analyze the intermolecular binding energy (Ebind) of the composite system. DAAF/FOX‐7 with a mass ratio of 90:10 shows a higher Ebind (183.24 kJ mol−1) and peak temperature at the heating rate of 0 °C min−1 (266.2 °C) than DAAF/FOX‐7 with a mass ratio of 70:30 and DAAF/FOX‐7 with a mass ratio of 80:20; this indicates that DAAF/FOX‐7 (90:10) shows better thermal stability. EXPLO5 is used to analyze the detonation velocity of the composite system, and the detonation velocity of DAAF/FOX‐7 microspheres increase by 0.5 km s−1 compared to that of DAAF. The characteristic drop height of impact sensitivity is more than 100 cm, and this demonstrates that the microspheres exhibit good safety performance. The morphology, crystal structure, thermal decomposition property, and impact sensitivity of the microspheres are investigated and compared. X‐ray diffraction and Fourier transform infrared spectroscopy results indicate that the structure of the DAAF/FOX‐7 composite is not changed compared to that of the raw material.